1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Someone help!

  1. Oct 17, 2004 #1
    OK this problem is probably really easy, but I totally have no idea how to handle it. Please help! Here goes:

    A 20kg cart on wheels has been pushed up against a wall with a spring (k= 244N/m) between the cart and the wall. If the spring is compressed a distance of 0.1m and a force of 20N is continued to be applied toward the wall, what will the acceleration of the object be?
  2. jcsd
  3. Oct 17, 2004 #2
    You know mass, you know k, you know dx, you know F.

    F = -kx = 1/2kx^2 = ma

    a = -kx/m
  4. Oct 17, 2004 #3
    One question: how come kx is negative?
  5. Oct 17, 2004 #4
    it is usually opposite to the direction of inertia
  6. Oct 17, 2004 #5
    OK thanks for the help!
  7. Oct 18, 2004 #6

    Doc Al

    User Avatar

    Staff: Mentor

    To find the acceleration of an object, use Newton's 2nd law. First find the net force on the cart. There are two (horizontal) forces on the cart: the spring, pushing out from the wall; and the applied force of 20 N pushing towards the wall. Find the net force and then calculate the acceleration [itex]a = F_{net}/m[/itex].

    The force law for springs: F = -kx, tells you the force that the spring exerts for a given stretch or compression x (from equilibrium). The negative sign means that the force is in the opposite direction of the compression. For example: If the spring is pushed in, the force it exerts pushes out.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook